The present invention relates to a watertight brushless fan motor.
Generally, the brushless fan motor includes a stator, a circuit substrate fixed to the stator, one or more electronic components mounted on the circuit substrate, and a rotor provided with a plurality of blades. In the brushless fan motor of this type, waterproofing of the stator, circuit substrate, and the like is demanded. As shown in Japanese Patent Application Laid-Open Publication No. 191611/1998, a watertight brushless fan motor was proposed in which a molded part was formed by molding with an insulating resin in such a manner that the electronic components and the circuit substrate are included therein. However, the molded part thus formed might expand or shrink, thereby damaging the electronic components and the circuit substrate. Actually, a protective layer, which alleviates the expansion or shrinkage of the molded part to prevent damage to the circuit substrate, is provided between the molded part and the circuit substrate with the electronic components mounted thereon. Among such prior arts is the one shown in Japanese Patent Application Laid-Open Publication No. 335800/1995, which is not applied to the motor, though.
Recently, an insulating resin having high adhesion strength such as urethane has become employed for the molded part so as to shorten its curing time and obtain a waterproofing effect at low cost. However, the molded part described above becomes more adhered to the electronic components. Thus, when the molded part has expanded or shrunk due to a change in temperature, the molded part acts to pull off the electronic components from the circuit substrate. Consequently, electrical connection between the electronic components and circuits on the circuit substrate might be broken. Further, when the molded part described above was formed, the breakage of electrical connection between the electronic components and the circuits on the circuit substrate could not be prevented merely by providing the conventional protective layer between the circuit substrate and the molded part.
The prevent invention has been made to solve the problems described above. It is therefore an object of the present invention to provide a watertight brushless fan motor that can prevent breakage of electrical connection between electronic components and circuits on a circuit substrate, caused by a molded part.
Another object of the invention is to provide a watertight brushless fan motor that can prevent the molded part from coming into contact with a rotor when the molded part has expanded.
A watertight brushless fan motor to which the present invention aims at improvement includes a circuit substrate fixed to a stator, one or more electronic components mounted on the circuit substrate, a rotor including a plurality of blades, and a molded part formed of an insulating resin in such a manner that the stator, the one or more electronic components, and the circuit substrate are included therein.
The molded part, when having been formed to directly cover the electronic components and the circuit substrate and expanding or shrinking due to a change in temperature, expands or shrinks to such an extent that electrical connection between the electronic components and circuits on the circuit substrate might be broken. In the present invention, the watertight brushless fan motor further includes a protective layer provided at least between the one or more electronic components and the molded part, for preventing the breakage of electrical connection that might occur due to the expansion or shrinkage of the molded part. Then, shear adhesion strength and thickness of the protective layer are defined so that, when the expansion or shrinkage that might cause the breakage of electrical connection has occurred, separation between the one or more electronic components and the protective layer can be caused.
More specifically, a watertight brushless fan motor to which the present invention aims at improvement includes a stator having a plurality of stator magnetic poles and comprising an iron core having a plurality of projecting pole portions and a winding wound around each projecting pole portion of the iron core. The iron core is constituted from a plurality of laminated steel plates.
The watertight brushless fan motor further comprises: a circuit substrate fixed to the stator with a predetermined space provided between the circuit substrate and the projecting pole portions; one or more electronic components mounted on the circuit substrate so as to constitute a control circuit for controlling current flowing through the windings; a rotor including a plurality of rotor magnetic poles, each of which is made of a permanent magnet, on an inner peripheral side thereof and including a plurality of blades on an outer peripheral side thereof; a case; and a molded part.
The case includes an inner cylindrical section, a plate-like section, and an outer cylindrical section. The inner cylindrical section includes bearing for rotatably supporting the rotary shaft of the rotor. The plate-like section extends from an end of the inner cylindrical section in a direction perpendicular to the center line of the inner cylindrical section with a predetermined space provided between the plate-like section and the circuit substrate. The outer cylindrical section extends in the axial line direction of the rotary shaft from an outer end of the plate-like section, along the inner cylindrical section. In the present invention, a protective layer is formed of an insulating material having shear adhesion strength smaller than the sear adhesion strength of the insulating resin that has been cured, and the shear adhesion strength and the thickness of the protective layer are defined so that, when the expansion or shrinkage that might cause the breakage of electrical connection has occurred, separation between the one or more electronic components and the protective layer can be caused. For example, when the insulating resin for forming the molded part, which has been cured, has a shear adhesion strength of 30 kfg/cm2 or more, the insulating material that forms the protective layer having a shear adhesion strength of 15 kgf/cm2 or less should be employed, and the protective layer should have a thickness in the range of 10 xcexcm to 50 xcexcm. The xe2x80x9cshear adhesion strengthxe2x80x9d herein refers to the strength under which joined surfaces break away by applying a shear stress to the joined surfaces, as defined in the JIS-K6800.
When the shear adhesion strength and the thickness of the protective layer are defined as in the present invention, separation between the one or more electronic components and the protective layer occurs even if the molded part has expanded or shrunken due to a change in temperature. Thus, separation of the electronic components from the circuit substrate due to the expansion or shrinkage of the molded part can be prevented. For this reason, the breakage of electrical connection between the electronic components and the circuits on the circuit substrate can be prevented.
Preferably, the protective layer is formed so as to cover the entire surface of the circuit substrate including the one or more electronic components. With this arrangement, the protective layer can be easily formed by spraying over the entire surface of the circuit substrate with the electronic components mounted thereon.
Various materials can be employed as the insulating resin for forming the molded part and the protective layer. If the insulating resin for forming the molded part is made of an urethane resin, for example, a silicon resin can be employed for the protective layer.
In a watertight brushless fan motor according to another aspect of the present invention, at least one concave portion is provided in a portion of the surface of the molded part that faces the rotor, so as to be open toward the rotor and to receive expansion of the molded part in order to prevent contact of the molded part with the rotor when the molded part has expanded. When at least one concave portion is formed in the molded part in this manner, the expansion of the molded part is received by the concave portion, even if the molded part has expanded due to a change in temperature. Thus, contact of the molded part with the rotor is prevented.
Notably, there are not many electronic components inside the outer cylindrical portion. Accordingly, the thickness of the molded part inside the outer cylindrical portion increases. For this reason, the concave portion is preferably formed of an annular groove formed to be adjacent to and run along the outer cylindrical section.
As a matter of course, the watertight brushless fan motor can be configured to have both the concave portion thus formed and the protective layer described above.
According to the present invention, when the molded part has expanded or shrunken due to a change in temperature, separation between the one or more electronic components and the protective layer occurs. Thus, separation of the electronic components from the circuit substrate due to the molded part can be prevented. For this reason, the breakage of electrical connection between the electronic components and the circuits on the circuit substrate can be prevented.
According to the present invention, at least one concave portion is formed in the molded part. Thus, even if the molded part has expanded due to a change in temperature, the expansion of the molded part is received by the concave portion, so that contact of the molded part with the rotor is prevented.